Recently a paper was published in Ultrasound in Medicine and Biology showing absence of the second systolic peak in patients with severe sepsis.
The paper can be found at: sciencedirect.com
These findings illustrate how important it is to discriminate a first and second systolic phase in pulsatile signals such as arterial blood pressure or intra arterial blood flow velocity.
The graph above shows (age corrected) Z-scores for a group of 16 patients before (red) and after (yellow) fluid resuscitation. All patients had high Z-scores for all parameters before as well as after fluid resuscitation. Fluid resuscitation increased the Sys1 and Sys2 components, allowing a slight decrease in HR.
These high Z-scores for Sys1, Sys2 and Dias@560 may implicate a diffuse loss of cerebral arteriolar resistance, either due to low blood pressure or because of circulating endotoxins.
The blood flow velocities measured by TCD are complex signals but can give instantaneous information about cerebral hemodynamics. Neuromon B.V. aims to disclose this information in a meaningful way to physicians for rapid diagnostic and therapeutic purposes. At the beginning of 2018 Neuromon B.V. presented a novel approach for graphical representation of the middle cerebral artery flow velocity. Based upon the improved parameters Z-scores are calculated to correct for age and different variables are combined into a single radar-plot.
The background of this graphical representation is explained in the following pamflet: TCD-NewParmCoordinates.pdf.
This app intends to bridge the gap between middle cerebral artery flow velocity parameterisation and clinical interpretation. Basically, sys1, sys2, dias@560 and HR are converted to so-called Z-scores that correct for the effects of ageing.
Based upon published observations the Z-scores are used for clinical interpretation. Of course, Neuromon BV cannot take the responsibility for clinical decision making and the NMA app should only be seen as support in the process. Treating physicians should always remain vigilant and not use information from the NMA alone to interpret the clinical condition of a patient. Nevertheless, the NMA module brings a new approach to patient assessment on the ICU based upon a new philosophy on cardiovascular physiology.
Find your NMA in the Appstore via this link NMA or alternatively by searching "NMA TCD".
In a joint effort DWL and Neuromon B.V. have recently made the new TCD parameters available for current and future DWL customers. In the latest QL software signal analysis based upon the new TCD parameters is optionally available. It can be acquired via the DWL distributors network. The new TCD parameters significantly enhance signal analysis and interpretation. Please refer to relevant literature.
Middle cerebral artery flow velocity decreases with age. When studying subjects with transcranial Doppler, these age-related changes should be taken into account. A recent paper by dr. A. Schaafsma promotes Z-scores as a way to correct for age. Z-scores express the distance in standard deviations to the middle cerebral artery flow velocity expected for age by linear regression.
A Z-score expresses how many standard deviations a given measurement is above (positive) or below (negative) the value expected for a given age. Z-scores for different parameters can be combined into a radar plot. An example is give to the right: data are provided for average Z-scores during hyperventilation (red), normoventilation (green) and CO2-retention (yellow).
A. Schaafsma, A new method for correcting middle cerebral artery flow velocity for age by calculating Z-scores. Journal of Neuroscience Methods. 307, 1–7 (2018).